In charged particle beam (CPB) systems, specimens or “workpieces” are retained on movable stages for positioning relative to the beam. Charged particle beam systems are used in a plurality of industrial fields, including, but not limited to, testing systems, imaging systems like scanning electron microscopes (SEMs), inspection systems for semiconductor devices, and exposure systems for pattern writing via lithography.
There is a high demand for structuring, testing and inspecting specimens within the micrometer and nanometer scale. Micrometer and nanometer scale process control, inspection or structuring is often done with charged particle beams, e.g. electron beams. Charged particle beams offer superior spatial resolution compared to, e.g. photon beams, due to their short wavelengths. However, there are also light optical systems with a stage that supports a specimen and the stage being movable to position the specimen with a precision of 50 nm or better.
Generally, as the precision of measurement, testing, or patterning systems increases there is a demand for high precision and fast positioning of specimen in those system. The stage holding the specimen is typically independently movable in x-direction and y-direction. In conventional systems, positioning data of the stage is measured in two perpendicular axes (e.g., X and Y axes). The electron beam of the e-beam inspection tool is deflected by a vector opposite to that of the measured error in position.
Unfortunately, prior art systems typically assume a negligible effect of pitch and roll and assume a fixed primary beam with respect to the plane of interest. However, in practice, the effects of pitch and roll may be significant and result in significant positional errors. Further various sources may also cause movement of the primary beam, which may also result in significant positional error.
Accordingly, what is needed is improved systems for detecting positions of moving stages and accurately compensating position error during operation (in “real time”).